Indexing? It's a tough job but someone's gotta do it. That said, I largely agree with the sentiment expressed below. I guess the way I would express it isn't "reflecting how the reader thinks" so much as establishing categories (or stepping stones?) of content that the reader can then plow through.
The role of the index in digital products has become a subject of heated debate when information professionals gather to formalize standards. Some publishers and authors are under the misguided impression that a full-text search can replace the traditional subject index. The American Society for Indexing (ASI) has spent the last few years reminding the world that a good index is not just a concordance; it adds value to a digital object beyond the basic word search. An index created by a good indexer reflects how the reader thinks and offers entry points that may not be written in the text. With increased attention on analytics and search, there is also a strong argument to be made that indexes are more important for digital publications than print ones.
Badgett, Nan. Medford, NJ. "A Review of "The Accidental Indexer", Information Today, 2015, 240 pp. http://dx.doi.org/10.1080/19322909.2016.1229075